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A. Heuberger

Bio: A. Heuberger is an academic researcher. The author has contributed to research in topics: Etching (microfabrication) & Crystalline silicon. The author has an hindex of 2, co-authored 2 publications receiving 2007 citations.

Papers
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TL;DR: In this article, the anisotropic etching behavior of single-crystal silicon and the behavior of and in an ethylenediamine-based solution as well as in aqueous,, and were studied.
Abstract: The anisotropic etching behavior of single‐crystal silicon and the behavior of and in an ethylenediaminebased solution as well as in aqueous , , and were studied. The crystal planes bounding the etch front and their etch rates were determined as a function of temperature, crystal orientation, and etchant composition. A correlation was found between the etch rates and their activation energies, with slowly etching crystal surfaces exhibiting higher activation energies and vice versa. For highly concentrated solutions, a decrease of the etch rate with the fourth power of the water concentration was observed. Based on these results, an electrochemical model is proposed, describing the anisotropic etching behavior of silicon in all alkaline solutions. In an oxidation step, four hydroxide ions react with one surface silicon atom, leading to the injection of four electrons into the conduction band. These electrons stay localized near the crystal surface due to the presence of a space charge layer. The reaction is accompanied by the breaking of the backbonds, which requires the thermal excitation of the respective surface state electrons into the conduction band. This step is considered to be rate limiting. In a reduction step, the injected electrons react with water molecules to form new hydroxide ions and hydrogen. It is assumed that these hydroxide ions generated at the silicon surface are consumed in the oxidation reaction rather than those from the bulk electrolyte, since the latter are kept away from the crystal by the repellent force of the negative surface charge. According to this model, monosilicic acid is formed as the primary dissolution product in all anisotropic silicon etchants. The anisotropic behavior is due to small differences of the energy levels of the backbond surface states as a function of the crystal orientation.

1,529 citations

Journal ArticleDOI
TL;DR: In this article, the etching behavior of highly boron doped silicon in aqueous solutions based of ethylenediamine, KOH, NaOH, and LiOH was studied.
Abstract: The etching behavior of highly boron doped silicon in aqueous solutions based of ethylenediamine, KOH, NaOH, and LiOH was studied. For all etchants, a strong reduction of the etch rate for boron concentrations exceeding approximately 2 �9 10 ~9 cm -3 was observed. This value is in good agreement with published data for the onset of degeneracy of p-type silicon. The reduction of the etch rate was found to be inversely proportional to the fourth power of the boron concentration. For a given high boron concentration, the etch stop effect was found to be most effective for ethylenediamine-based solutions and low concentration KOH and least effective for highly concentrated KOH. On the basis of these results, a model is proposed attributing the etch stop phenomenon to electrical effects of holes rather than chemical effects of boron. Due to the high dopant concentration the width of the space charge layer on the silicon surface shrinks drastically. Therefore, electrons injected into the conduction band by an oxidation reaction cannot be confined to the surface and rapidly recombine with holes from the valence band. The lack of these electrons impedes the reduction of water and thereby the formation of new hydroxide ions at the silicon surface. Since the transfer of four electrons is required for the dissolution of one silicon atom the observed fourth power law for the decrease of the etch rate can be explained. The reduction of the etch rate on silicon doped with germanium or phosphorus is much smaller and follows a different mechanism.

519 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the etch rates of 53 materials that are used or potentially can be used or in the fabrication of microelectromechanical systems and integrated circuits were prepared.
Abstract: Samples of 53 materials that are used or potentially can be used or in the fabrication of microelectromechanical systems and integrated circuits were prepared: single-crystal silicon with two doping levels, polycrystalline silicon with two doping levels, polycrystalline germanium, polycrystalline SiGe, graphite, fused quartz, Pyrex 7740, nine other preparations of silicon dioxide, four preparations of silicon nitride, sapphire, two preparations of aluminum oxide, aluminum, Al/2%Si, titanium, vanadium, niobium, two preparations of tantalum, two preparations of chromium, Cr on Au, molybdenum, tungsten, nickel, palladium, platinum, copper, silver, gold, 10 Ti/90 W, 80 Ni/20 Cr, TiN, four types of photoresist, resist pen, Parylene-C, and spin-on polyimide. Selected samples were etched in 35 different etches: isotropic silicon etchant, potassium hydroxide, 10:1 HF, 5:1 BHF, Pad Etch 4, hot phosphoric acid, Aluminum Etchant Type A, titanium wet etchant, CR-7 chromium etchant, CR-14 chromium etchant, molybdenum etchant, warm hydrogen peroxide, Copper Etchant Type CE-200, Copper Etchant APS 100, dilute aqua regia, AU-5 gold etchant, Nichrome Etchant TFN, hot sulfuric+phosphoric acids, Piranha, Microstrip 2001, acetone, methanol, isopropanol, xenon difluoride, HF+H/sub 2/O vapor, oxygen plasma, two deep reactive ion etch recipes with two different types of wafer clamping, SF/sub 6/ plasma, SF/sub 6/+O/sub 2/ plasma, CF/sub 4/ plasma, CF/sub 4/+O/sub 2/ plasma, and argon ion milling. The etch rates of 620 combinations of these were measured. The etch rates of thermal oxide in different dilutions of HF and BHF are also reported. Sample preparation and information about the etches is given.

1,256 citations

Journal ArticleDOI
28 Sep 2012-Science
TL;DR: A set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior are reported, together with integrated sensors, actuators, power supply systems, and wireless control strategies.
Abstract: A remarkable feature of modern silicon electronics is its ability to remain physically invariant, almost indefinitely for practical purposes. Although this characteristic is a hallmark of applications of integrated circuits that exist today, there might be opportunities for systems that offer the opposite behavior, such as implantable devices that function for medically useful time frames but then completely disappear via resorption by the body. We report a set of materials, manufacturing schemes, device components, and theoretical design tools for a silicon-based complementary metal oxide semiconductor (CMOS) technology that has this type of transient behavior, together with integrated sensors, actuators, power supply systems, and wireless control strategies. An implantable transient device that acts as a programmable nonantibiotic bacteriocide provides a system-level example.

1,026 citations

Journal ArticleDOI
TL;DR: The etch rates for 317 combinations of 16 materials (single-crystal silicon, doped, and undoped polysilicon, several types of silicon dioxide, stoichiometric and silicon-rich silicon nitride, aluminum, tungsten, titanium, Ti/W alloy, and two brands of positive photoresist) used in the fabrication of microelectromechanical systems and integrated circuits in 28 wet, plasma, and plasmaless-gas-phase etches (several HF solutions, H/sub 3/PO/sub 4), HNO/sub
Abstract: The etch rates for 317 combinations of 16 materials (single-crystal silicon, doped, and undoped polysilicon, several types of silicon dioxide, stoichiometric and silicon-rich silicon nitride, aluminum, tungsten, titanium, Ti/W alloy, and two brands of positive photoresist) used in the fabrication of microelectromechanical systems and integrated circuits in 28 wet, plasma, and plasmaless-gas-phase etches (several HF solutions, H/sub 3/PO/sub 4/, HNO/sub 3/+H/sub 2/O+NH/sub 4/F, KOH, Type A aluminum etchant, H/sub 2/O+H/sub 2/O/sub 2/+HF, H/sub 2/O/sub 2/, piranha, acetone, HF vapor, XeF/sub 2/, and various combinations of SF/sub 6/, CF/sub 4/, CHF/sub 3/, Cl/sub 2/, O/sub 2/, N/sub 2/, and He in plasmas) were measured and are tabulated. Etch preparation, use, and chemical reactions (from the technical literature) are given. Sample preparation and MEMS applications are described for the materials.

930 citations

Journal ArticleDOI
01 Aug 1998
TL;DR: In this article, the available etching methods fall into three categories in terms of the state of the etchant: wet, vapor, and plasma, and they are reviewed and compared by comparing the results, cost, complexity, process compatibility, and other factors.
Abstract: Bulk silicon etching techniques, used to selectively remove silicon from substrates, have been broadly applied in the fabrication of micromachined sensors, actuators, and structures. Despite the more recent emergence of higher resolution, surface-micromachining approaches, the majority of currently shipping silicon sensors are made using bulk etching. Particularly in light of newly introduced dry etching methods compatible with complementary metal-oxide-semiconductors, it is unlikely that bulk micromachining will decrease in popularity in the near future. The available etching methods fall into three categories in terms of the state of the etchant: wet, vapor, and plasma. For each category, the available processes are reviewed and compared in terms of etch results, cost, complexity, process compatibility, and a number of other factors. In addition, several example micromachined structures are presented.

780 citations